Abstract

A suction electrode for establishing electrical contact between living tissue and an electrical conductor. The electrode comprises a cup-shaped member that terminates in an opening defined by a peripheral lip having a minimum radius of about 0.015 inch. An interior cavity defined by the member has a depth at least 0.5 times the diameter of the opening and includes an evacuation port opposite from the opening. Air channels or grooves depressed into the cavity surface connect the evacuation port with remote portions of the cavity to facilitate the evacuation process even if tissue is drawn into contact with the cavity walls. Surfaces of the member coming into contact with the tissue have a relatively rough surface finish and the member includes means for connection to an electrical conductor or the like.

Primary Exaniiner--Richard A. Gaudet Assistant E.raminerLee S. Cohen Attorney, Agenl, 0r FirmTownsend and Townsend [57] ABSTRACT A suction electrode for establishing electrical contact between living tissue and an electrical conductor. The electrode comprises a cup-shaped member that terminates in an opening defined by a peripheral lip having a minimum radius of about 0.015 inch. An interior cavity defined by the member has a depth at least 0.5 times the diameter of the opening and includes an evacuation port opposite from the opening. Air channels or grooves depressed into the cavity surface connect the evacuation port with remote portions of the cavity to facilitate the evacuation process even if tissue is drawn into contact with the cavity walls. Surfaces of the member coming into contact with the tissue have a relatively rough surface finish and the member includes means for connection to an electrical conductor or the like.

3 Claims, 5 Drawing Figures 1 SUCTION ELECTRODE BACKGROUND OF THE INVENTION The present invention relates to suction electrodes of the type employed in electrocardiography and similar applications in which electrical contact must be made with living tissue, e.g., with a patients skin. U.S. Pat. No. 2,580,628 generally discloses a suction electrode which comprises a spherically-shaped cup that is no greater than a hemisphere and that terminates in straight edges defining an access opening to the interior of the cup. The cup member includes an evacuation port for connection with an evacuating member such as a rubber bulb and a clamp for connection with an electrical conductor. This prior art cup is applied by placing it against the patient's skin, compressing the rubber bulb, and releasing the bulb so that a vacuum formed with the cup cavity draws the cup against the patients skin to thereby form an electric connection from the clamp to the skin via the cup member.

This prior artdevice', though a substantial improvement over earlier electrodes that had to be strapped or taped against the patient's skin and which were, therefore, cumbersome to use, still is less than fully satisfactory. A primary deficiency of the electrode is its relatively low holding power and a resulting tendency to fall off when applied to upright portions of a patients torso, for example, due to its own weight and that of electrical conductors secured to it. The problem is aggravated by the frequent use of electrolytic paste or surgical gel which enhances the electrical contact formed but which also renders the patientsskin more slippery.

It appears that a number of factors account for the inadequate holding force of such prior art electrodes. With an increasing shallowness of the electrode cavity, the holding power appears to decrease for a given vacuum and electrode aperture diameter. Thus, I have found that in instances in which the cavity depth is about 0.4 times the access opening diameter the electrodes holding power is frequently insufficient to retain the electrodes to the encountered unevenness and curvature of inclined skin portions. Although initially it seems to be unlikely that the cavity depth has much influence on the electrodes holding power, it appears that when skin is drawn into the evacuated cavity it can prematurely block the evacuation port when the cavity is relatively shallow. This causes the entrapment of air bubbles which reduce the total holding force. The straight downwardly facing sidewalls of this prior art suction electrode further appear to offer relatively little resistance against lateral electrode sliding, particularly when the total holding force is relatively low and the underlying skin is lubricated with electrolytic paste.

SUMMARY OF THE INVENTION The present invention provides a suction electrode which overcomes the shortcomings encountered with prior art suction electrodes. In particular, it develops a holding force which greatly exceeds the holding force that can be developed with prior art electrodes without increasing the formed vacuum or causing patient discomfort from excess vacuums, sharp edges and the like.

Generally speaking, a suction electrode for establishing a firm and secure electrical contact with living tissue constructed in accordance with the present inven- LII tion comprises a generally cup-shaped member that has a hollow interior cavity and a continuous sidewall forming a portion of the interior. Free ends of the sidewalls terminate in a skin-contacting surface and an inwardly projecting peripheral lip which defines an access opening that communicates the cavity with the exterior of the member. Means is provided for forming an evacuation port that is spaced from the opening for connection of the cavity with an evacuator such as a rubber bulb. A plurality of grooves are disposed in the portion of the member defining the inner space and each groove is adjacent the port and connected therewith so that the grooves aid the evacuation of the cavity. Free groove ends are spaced from the access opening and the port. The cavity depth, that is the straight line distance between the access opening and the port exceeds about one-half the minimum transverse dimension of the opening and is preferably between 0.5 to 1.2 such transverse dimension. Greatest holding forces are obtained when the cavity depth is in the vicinity of about 0.75 the access opening diameter. Means is also provided for connecting the conductor to the member.

This suction electrode develops a substantially greater holding force than could be attained with prior art electrodes. The relatively great depth of the cavity allows the formation of a substantial vacuum without filling out the interior space with tissue drawn into the cup-shaped interior. I have determined with a cavity depth of about 0.6 times the access opening diameter the holding force developed by my suction electrode is between about 15 to 30 percent greater than the holding force developed by the earlier discussed prior art suction electrode. An even greater holding force differential is obtained when the cavity depth is increased to about 0.75 times the access hole diameter. Thereafter, an increase of the depth beyond about 0.75 times the access hole diameter causes a gradual decline of the holding force as depth approaches and exceeds the access opening diameter until, at a ratio of about 1.2 it is about equal to the holding force exerted at a cavity depth to opening ratio of about 0.5.

Even in instances in which the cavity depth is relatively low, say in the vicinity of 0.5 times the access hole diameter or less, the provision of the air evacuation grooves in the ceiling of the cavity which communicate with the evacuation port substantially enhance the holding power of the electrode of the present invention. This appears to be a result of eliminating a prem ature blocking of the evacuation port by tissue drawn into the cavity.

A yet further increase in the holding power of the suction electrode is obtained from the provision of a peripheral lip at the access opening. Tests have indicated that the suction electrode of the present invention resists lateral sliding on human tissue with a force of from 2 to 3 times greater than the force generated by the above-discussed prior art suction electrode. In part this seems to be a result of the greater holding force and/or vacuum developed within theelectrode of the present invention. However, this greater resistance to lateral sliding also appears to result to a substantial extent from the provision of the peripheral lip.

In the past it has been suggested to incorporate such peripheral lip. However, in practice they have not been generally accepted, at least in part since they provide discomfort whenever a signficant vacuum is formed in the cavity since the lips have a tendency to restrict blood circulation at least in the skin layers immediately underlying the lip. This problem has been eliminated in the lip of the present invention since this lip has a minimum radius of about 0.0l inch. The lip contact surface against the inwardly drawn skin is thereby sufficiently enlarged so that it ceases to be a source of patient discomfort.

A still further advantage provided by the suction electrode of the present invention is derived from the relatively rough interior surface finish of the suction cup. In a preferred embodiment of the invention the surface finish is in the range of about 350 to 20,000 micro inches (p. to about 350p.) as measured with a Profilometer or Brush Surface Analyzer in accordance with the ASA B46.l-l962 standard. Such a finish can be obtained with 600 to 50 grit sandpaper or sandblast, for example. The use of a surface finish within the stated range substantially enhances the resistance of the electrode against lateral sliding on living tissue irrespective of whether or not electrolytic paste is employed.

Thus, the suction electrode of the present invention represents a substantial improvement over such prior art electrodes. It is readily applied and it greatly reduces if not eliminates the danger that an electrode becomes disengaged from tissue during a test such as during electrocardiography.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation, partially in section, of a suction electrode constructed in accordance with the present invention;

FIG. 2 is a bottom end view of the electrode illustrated in FIG. 1;

FIG. 3 is a fragmentary, enlarged detail of a sidewall of the electrode and a peripheral lip defining the access opening of the electrode;

FIG. 4 is a bottom end view similar to FIG. 2 but illustrates another embodiment of the invention; and

FIG. 5 is a bottom end view similar to FIG. 4 of yet another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1-3, a suction electrode 2 constructed in accordance with the present invention generally comprises a main body 4 having a cup-shaped hollow interior cavity 6, a resilient bulb 8 secured to an evacuation port I0 of the body and a connector 12 for releasably securing an electrical conductor 14 (schematically shown in FIG. I only) to the electrode. The evacuation bulb is of a conventional construction and includes a neck 16 that embraces an exterior surface 18 of the evacuation port in an upright manner. As is well known when the bulb is compressed and body 4 placed against a compliant surface such as living tissue, release of the bulb draws air from the interior of the body into the interior of the bulb. When access opening 20 is closed off with the compliant material a partial vacuum (hereinafter vacuum) is formed in the hollow interior thus biasing the body against the tissue with a force that is a function of both the diameter of the access opening and the effective vacuum in the hollow electrode interio r.

The electrode may be constructed of metal or of an electrically non-conductive material such as plastic. ll constructed of plastic electrode surfaces that come in contact with the skin are metal plated or otherwise rendered electrically conducting and a suitable electric connection is made from connector 12 to the plated surfaces.

In the presently preferred embodiment of the invention the electrode body 4 has a generallly circular cross-section and a resulting generally cylindrical exterior configuration. Cavity 6 has a mushroom-like shape and is defined by an interior surface 22 which is spheri cally shaped, resulting in a generally hemispherical cavity. For the purposes of this specification and the claims. the term hemispherical is intended to mean a shape which approximates a hemisphere. The term is not intended, however, to limit the shape to the precise geometrical configuration of a hemisphere. Rather, it is intended to and does refer to a geometric body that approximates a hemisphere even though it might be defined by surfaces that are not spherical in shape and/or which defines a geometrical body which is more than one-half a sphere.

Access opening 20 is disposed opposite from evacuation port 10, is circular and is defined by an inwardly projecting peripheral lip 24. The lip is at a lower end 26 of cylindrical sidewalls 28 and terminates in an edge that is rounded and has a minimum radius R of 0.015 inch.

A plurality of elongate, equally spaced grooves 30 are depressed into interior surfaces 22 and extend radially away from evacuation port 10 and have first ends which communicate with the port. The grooves terminate in free ends 32 which are spaced from both the evacuation port and access opening 20. In the presently preferred embodiment of the invention the grooves have a width'of about one sixty-fourth to one thirtysecond of an inch with a minimum depth of at least about 0.010 inch and preferably of between one sixtyfourth to one thirty-second of an inch for purposes more fully described hereinafter.

Referring briefly to FIG. 4, in another embodiment of the invention the electrode 2 is constructed identical to the one illustrated in FIGS. 1 and 2 except for the arrangement of the grooves. Instead of a star-shaped array of grooves, a pair of aligned grooves 34 extend in opposite directions away from the evacuation port and terminate in an annular groove 36 that interconnects the free ends of the aligned grooves.

Turning now to the use of the suction electrode 2 of the present invention and referring to FIGS. 1-4, conductor 14 is coupled to connector 12 by inserting it in a receptacle hole 38 and an attendant grasps bulb 8 and compresses it. The electrode is placed against the patients skin so that end faces or surfaces 40 rest against the skin and the bulb is released. A vacuum is thereby formed within cavity 6 of the electrode which draws in tissue and causes atmospheric pressure to bias the electrode into intimate contact with the patients skin, the electrical contact being primarily formed by interior cavity walls 22 and the radiused peripheral lip 24. Depending upon the relative volumes between the bulb and the electrode interior, the bulb resiliency and the resulting vacuum, the patients skin is drawn into the electrode interior to a greater or lesser extent. Even if the shape of the electrode interior and the vacuum is such that the patients skin is pulled into contact with the interior surfaces 22 and against evacuation port 10 a complete evacuation of the hollow interior is still possible since the evacuation grooves 30, 34 and 36 provide fluid communication from the electrode interior to the evacuation port. With the above-mentioned minimum groove depth, blockage of the grooves by drawnin skin is avoided. Consequently, the formation of relatively high pressure air pockets in the cavity is avoided. A uniform and maximum holding force for the electrode is thus achieved.

As already referred to in the earlier portions of this specification, the holding force is maximized when the cavity depth H is about 0.75 times the diameter D of access opening 20. Good results have been obtained when this ratio between H and D is from 0.5 to 1.2. A ratio of 0.6 is desirable in that it avoids an excessive undercut of the electrode cavity with respect to the access opening and lip 24 and thus assures that the skin contacts substantially the entire cavity surface 22. Furthermore, a relatively small undercut facilitates contact of the skin with the entire cavity surface 22 and the ease with which the electrode is mass produced, e.g.

cast.

As already referred to above, the holding force of the electrode is further increased by providing surfaces in contact with the patients skin with a relatively rough surface finish such as the 350 to 20,000 micro inch range surface finish. Surfaces provided with such a roughened finish are the surfaces of lip 24 and at least portions of interior surfaces 22 defining cavity 6.

Referring now briefly to FIG. 5, in another embodiment of the invention an electrode 42 which is generally constructed in the same manner as electrode 2 illustrated in FIGS. 1-3 has a body 44 of an elongate configuration. The resulting access opening 46 is elongate, e.g. generally rectangular or elliptical and leads to a similarly shaped electrode cavity 48. As above described the electrode cavity communicates with the interior of an evacuation bulb 50 through an evacuation port 52 constructed as above described. In all other respects including its operation, the provision of air evacuation grooves 54, a peripheral lip 56, a rough surface finish and the like, this electrode is identical to the one illustrated in FIGS. 13.

I claim:

1. A suction electrode comprising a cup having an electrically conductive interior surface, the cup terminating in a continuous inwardly directed edge defining an aperture providing access to the surface, a termial point of the edge having a minimum radius of about 0.015 inch, the cup having an interior transverse dimension in a plane parallel to the aperture which is larger than a corresponding transverse dimension of the aperture, the interior surface further having a depth measured from the aperture which is about 0.75 times a transverse dimension of the aperture, means disposed approximately opposite from the aperture for evacuating the cup, and means for connecting the surface with an electrical conductor.

2. A suction electrode for releasably adhering to living tissue and the like and forming a firm and secure electrical contact from an electrical conductor to the tissue comprising a member having a hollow interior, and an electrically conductive continuous sidewall defining a portion of the interior and terminating in an end of the member, an inner portion of the sidewalls adjacent the end defining an inwardly extending peripheral lip terminating in an edge which in turn defines a generally round opening communicating the interior with the exterior of the member, the edge having a minimum radius of about 0.015 inch, the sidewall having a surface finish of between about 350 to 20,000 micro inches, an evacuator means defining an evacuation port spaced from the opening and connecting the interior space with said evacuator, a plurality of grooves defined by the member and being formed into the interior portion of the member defining the inner space, an end of each groove communicating with the port so that the grooves aid the evacuation of the inner space, another free end of the grooves being spaced from the opening, a straight line distance between the opening and the port being about 0.75 times the diameter of the opening, and means for connecting the conductor to the sidewall.

3. A suction electrode for releasably adhering to living tissue for forming a firm and secure electrical contact from an electrical conductor to the tissue comprising a member having a hollow interior and an electrically conductive sidewall defining a portion of the interior and terminating in an end of the member, an inner portion of the sidewall adjacent the end defining an inwardly extending peripheral lip terminating in an edge which in turn defines a generally round opening communicating the interior with the exterior of the member, the edge having a minimum radius of about 0.015 inch, the interior sidewall having a maximum spacing in a plane parallel to the opening which exceeds the diameter of the opening so as to define an undercut, the sidewall having a surface finish of between about 350 to 20,000 micro inches at least in the vicinity of the edge, an evacuator, means defining an evacuation port spaced from the opening and connecting the interior space with said evacuator, the interior space further having a depth measured from the opening which is about 0.75 times the diameter of the opening, and means for electrically connecting the conductor with the sidewall.

Claims (3)

1. A suction electrode comprising a cup having an electrically conductive interior surface, the cup terminating in a continuous inwardly directed edge defining an aperture providing access to the surface, a termial point of the edge having a minimum radius of about 0.015 inch, the cup having an interior transverse dimension in a plane parallel to the aperture which is larger than a corresponding transverse dimension of the aperture, the interior surface further having a depth measured from the aperture which is about 0.75 times a transverse dimension of the aperture, means disposed approximately opposite from the aperture for evacuating the cup, and means for connecting the surface with an electrical conductor.

2. A suction electrode for releasably adhering to living tissue and the like and forming a firm and secure electrical contact from an electrical conductor to the tissue comprising a member having a hollow interior, and an electrically conductive continuous sidewall defining a portion of the interior and terminating in an end of the member, an inner portion of the sidewalls adjacent the end defining an inwardly extending peripheral lip terminating in an edge which in turn defines a generally round opening communicating the interior with the exterior of the member, the edge having a minimum radius of about 0.015 inch, the sidewall having a surface finish of between about 350 to 20,000 micro inches, an evacuator means defining an evacuation port spaced from the opening and connecting the interior space with said evacuator, a plurality of grooves defined by the member and being formed into the interior portion of the member defining the inner space, an end of each groove communicating with the port so that the grooves aid the evacuation of the inner space, another free end of the grooves being spaced from the opening, a straight line distance between the opening and the port being about 0.75 times the diameter of the opening, and means for connecting the conductor to the sidewall.

3. A suction electrode for releasably adhering to living tissue for forming a firm and secure electrical contact from an electrical conductor to the tissue comprising a member having a hollow interior and an electrically conductive sidewall defining a portion of the interior and terminating in an end of the member, an inner portion of the sidewalL adjacent the end defining an inwardly extending peripheral lip terminating in an edge which in turn defines a generally round opening communicating the interior with the exterior of the member, the edge having a minimum radius of about 0.015 inch, the interior sidewall having a maximum spacing in a plane parallel to the opening which exceeds the diameter of the opening so as to define an undercut, the sidewall having a surface finish of between about 350 to 20,000 micro inches at least in the vicinity of the edge, an evacuator, means defining an evacuation port spaced from the opening and connecting the interior space with said evacuator, the interior space further having a depth measured from the opening which is about 0.75 times the diameter of the opening, and means for electrically connecting the conductor with the sidewall.